[Koha] Record Matching Rule for Path

Dear Koha Community, Could someone please offer advice on how to set up a record matching rule for path. We have spatial data indexed and for the tag 856(u) we have entered the directory path where the data is stored. This is the only unique identifier to match records to but we have had no success in setting up a record matching rule for the tag. We have the default record matching rules for ISSN and ISBN as well as one set up for title and these all work. We are uncertain as to the normalisation rule to enter as well as the search index. Any suggestions would be appreciated. Thankyou Regards, *Frances Sandeman* Library Technician